A wireless communication system has evolved to provide various high-speed large-capacity services to User Equipments (UEs). Examples of the wireless communication system include a Universal Mobile Telecommunications System (UMTS), a Global System for Mobile communications (GSM), a High Speed Downlink Packet Access (HSDPA) mobile communication system, a High Speed Uplink Packet Access (HSUPA) mobile communication system, a Long-Term Evolution (LTE) mobile communication system, an LTE-Advanced (LTE-A) mobile communication system, a High Rate Packet Data (HRPD) mobile communication system proposed by the 3rd Generation Partnership Project 2 (3GPP2), and an Institute of Electrical and Electronics Engineers (IEEE) 802.16m mobile communication system.
Cases in which a UE selects an LTE RAT or switches to the LTE RAT in a wireless communication system of the related art will be described below.
In a 3GPP mobile communication system, the UE selects the LTE RAT or switches to the LTE RAT if the UE performs a cell selection operation, a cell reselection operation, or a cell redirection operation, a description of which will be provided below.
FIG. 1 schematically illustrates a process for selecting an LTE RAT or switching to the LTE RAT if a UE performs a cell selection operation in a 3GPP mobile communication system according to the related art.
Prior to the description of FIG. 1, the cell selection operation is an operation in which the UE selects a RAT by blindly searching an LTE cell in a state in which the UE searches no cell. The cell selection operation is a RAT selection operation which is mainly used if the UE searches no cell signal or the UE is initially powered on.
Referring to FIG. 1, the 3GPP mobile communication system includes a UE 111, a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) 113, and an Evolved-UTRAN (E-UTRAN) 115.
If the UE 111 cannot acquire synchronization with a cell included in the UTRAN 113 or the UE 111 is initially powered on at operation 117, the UE 111 transits into an LTE RAT mode at operation 119. In the LTE RAT mode, the UE 111 performs a cell search operation at operation 121. The E-UTRAN 115 broadcasts cell information by a preset period at operation 123, and the UE 111 performs the cell search operation using the cell information broadcasted by the E-UTRAN 115. Here, the description of the cell search operation will be omitted.
After performing the cell search operation, the UE 111 performs an LTE cell camping operation with the UTRAN 113 and the E-UTRAN 115 at operation 125. The LTE cell camping operation includes an attach procedure, a tracking area update procedure, etc., and a detailed description of the attach procedure and the tracking area update procedure will be omitted.
After performing the LTE cell camping operation, the UE 111 acquires synchronization with an LTE cell neighboring the UE 111, so the UE 111 may select an LTE RAT as a RAT of the UE 111 or switch to the LTE RAT.
FIG. 2 schematically illustrates a process for selecting an LTE RAT or switching to the LTE RAT if a UE performs a cell reselection operation in a 3GPP mobile communication system according to the related art.
Referring to FIG. 2, the 3GPP mobile communication system includes a UE 211, a UTRAN 213, and an Evolved-UTRAN 215.
The UE 211 performs a cell search operation with the UTRAN 213 at operation 217. The UTRAN 213 broadcasts cell information by a preset period at operation 219, and the UE 211 performs the cell search operation using the cell information broadcasted by the UTRAN 213. Here, the description of the cell search operation will be omitted.
After performing the cell search operation, the UE 211 performs a 3G cell camping operation with the UTRAN 213 at operation 221. The detailed description of the 3G cell camping operation will be omitted.
After performing the 3G cell camping operation, the UE 211 acquires synchronization with a cell included in the UTRAN 213, and performs an Inter-RAT measurement operation as a switching operation from a UMTS scheme to an LTE scheme at operation 223. The E-UTRAN 215 broadcasts broadcasting information by a preset period at operations 225, 227, and 229, the broadcasting information may include various parameters, and the detailed description of the broadcasting information will be omitted. The UE 211 performs the Inter-RAT measurement operation using the broadcasting information broadcasted by the E-UTRAN 215, and the detailed description of the Inter-RAT measurement operation will be omitted.
After performing the Inter-RAT measurement operation, the UE 211 transits into an LTE RAT mode at operation 231. After transiting into the LTE RAT mode, the UE 211 performs a cell search operation at operation 233. The E-UTRAN 215 broadcasts cell information by a preset period at operation 235, and the UE 211 performs the cell search operation using the cell information broadcasted by the E-UTRAN 215. Here, the description of the cell search operation will be omitted.
After performing the cell search operation, the UE 211 performs an LTE cell camping operation with the UTRAN 213 and the E-UTRAN 215 at operation 237. The LTE cell camping operation includes a tracking area update procedure, etc., and the detailed description of the tracking area update procedure will be omitted.
After performing the LTE cell camping operation, the UE 211 acquires synchronization with an LTE cell neighboring the UE 211, so the UE 211 may select an LTE RAT as a RAT of the UE 211 or switch to the LTE RAT.
The cell reselection operation in a 3GPP mobile communication system of the related art as described in FIG. 2 is an operation in which a UE which is synchronized with a cell not an LTE cell switches a RAT by determining whether there is an LTE cell neighboring the UE through signal measurement, and acquiring a synchronization from the LTE cell neighboring the UE if there is the LTE cell neighboring the UE. So, the UE does not miss a paging signal targeting the UE using a RAT which the UE already used, and the UE may independently switch to the RAT.
FIG. 3 schematically illustrates a process for selecting an LTE RAT or switching to the LTE RAT if a UE performs a cell redirection operation in a 3GPP mobile communication system according to the related art.
Referring to FIG. 3, the 3GPP mobile communication system includes a UE 311, a UTRAN 313, and an Evolved-UTRAN 315.
The UE 311 performs a cell search operation with the UTRAN 313 at operation 317. The UTRAN 313 broadcasts cell information by a preset period at operation 319, and the UE 311 performs the cell search operation using the cell information broadcasted by the UTRAN 313. Here, the description of the cell search operation will be omitted.
After performing the cell search operation, the UE 311 performs a 3G cell camping operation with the UTRAN 313 at operation 321. The detailed description of the 3G cell camping operation will be omitted.
After performing the 3G cell camping operation, the UE 311 acquires synchronization with a cell included in the UTRAN 313, and receives a cell redirection command which commands the UE 311 to perform a cell redirection operation with the E-UTRAN 315 from the E-UTRAN 315 at operation 323. The E-UTRAN 315 may transmit the cell redirection command to the UE 311 in various cases, and the detailed description of the various cases will be omitted.
After receiving the cell redirection command from the E-UTRAN 315, the UE 311 transits into an LTE RAT mode at operation 325. In the LTE RAT mode, the UE 311 performs a cell search operation at operation 327. The E-UTRAN 315 broadcasts cell information by a preset period at operation 329, and the UE 311 performs the cell search operation using the cell information broadcasted by the E-UTRAN 315. Here, the description of the cell search operation will be omitted.
After performing the cell search operation, the UE 311 performs an LTE cell camping operation with the UTRAN 313 and the E-UTRAN 315 at operation 331. The LTE cell camping operation includes a tracking area update procedure, etc., and the detailed description of the tracking area update procedure will be omitted.
After performing the LTE cell camping operation, the UE 311 acquires synchronization with an LTE cell neighboring the UE 311, so the UE 311 may select an LTE RAT as a RAT of the UE 311 or switch to the LTE RAT.
FIG. 4 schematically illustrates a process for selecting an LTE RAT or switching to the LTE RAT if a UE performs a cell selection operation in a 3GPP mobile communication system according to the related art.
Referring to FIG. 4, the 3GPP mobile communication system includes a UE 411, a UTRAN 413, and an evolved-UTRAN 415.
If the UE 411 which is synchronized with a cell included in the UTRAN 413 determines to select an LTE RAT or switch to the LTE RAT, that is, the UE 411 detects that a Fast Return to LTE event occurs at operation 417, the UE 411 transits into an idle state as a Radio Resource Control (RRC) state at operation 419. The Fast Return to LTE event is an event which commands the UE 411 to quickly select an LTE RAT or quickly switch to the LTE RAT. The Fast Return to LTE event may occur according to a system situation of the 3GPP mobile communication system, and the detailed description of a situation in which the Fast Return to LTE event occurs will be omitted.
After transiting into the idle state, the UE 411 transits into an LTE RAT mode at operation 421. In the LTE RAT mode, the UE 411 performs a cell search operation at operation 423. The E-UTRAN 415 broadcasts cell information by a preset period at operation 425, and the UE 411 performs the cell search operation using the cell information broadcasted by the E-UTRAN 415. Here, the description of the cell search operation will be omitted.
After performing the cell search operation, the UE 411 performs an LTE cell camping operation with the UTRAN 413 and the E-UTRAN 415 at operation 427. The LTE cell camping operation includes an attach procedure, a tracking area update procedure, etc., and the detailed description of the attach procedure and the tracking area update procedure will be omitted.
After performing the LTE cell camping operation, the UE 411 acquires synchronization with an LTE cell neighboring the UE 411, so the UE 411 may select an LTE RAT as a RAT of the UE 411 or switch to the LTE RAT.
The Fast Return to LTE event as described in FIG. 4 is an event which is supported on a cell selection process in which a UE quickly transits into an LTE RAT mode, and the UE performs the cell selection process after forcibly transiting into the LTE RAT mode based on the decision of the UE at a specific time. If the UE forcibly transits into the LTE RAT mode based on the Fast Return to LTE event, the UE transits into the LTE RAT mode without performing additional procedures such as a procedure in which the UE demodulates cell information and a procedure in which the UE measures a signal, so the cell reselection process in FIG. 4 has an advantage which is a quick LTE RAT mode transition speed compared with the reselection process in FIG. 2, and an advantage which is an independent LTE RAT mode transition of the UE compare with the cell redirection process in FIG. 3.
The cell selection process in FIG. 4 is generally used for a fast LTE RAT switching at a time at which a Circuit Switched (CS) domain which is established after the UE switches from an LTE RAT to a UMTS/Global System for Mobile communications (GSM) RAT through a CS fallback is released.
However, the LTE RAT selecting operation or the LTE RAT switching operation described in FIGS. 1 to 4 has the following problems.
Firstly, the LTE RAT selecting operation or the LTE RAT switching operation described in FIGS. 1 to 3 has a limitation for a UE to frequently perform a fast LTE RAT selecting operation or a fast LTE RAT switching operation.
The LTE RAT selecting operation or the LTE RAT switching operation through a cell selection operation described in FIG. 1 may be only performed in a limited scenario such as a situation in which the UE is powered on or a situation in which the UE does not acquire synchronization with a cell. The LTE RAT selecting operation or the LTE RAT switching operation through a cell reselection operation described in FIG. 2 enables a relatively stable RAT switching. However, it is impossible to perform a fast LTE RAT selecting operation or a fast LTE RAT switching operation since it takes long time to demodulate broadcasted cell information and measure a signal. If an operation state of the UE is an RRC state in which an LTE cell signal measurement is impossible, switching to an LTE mobile communication system is impossible, so the LTE RAT selecting or the LTE RAT switching is also impossible. Further, the LTE RAT selecting operation or the LTE RAT switching operation through a cell redirection operation described in FIG. 3 may be only performed in a case that there is a command from a network, so the UE may not independently perform the LTE RAT switching operation or the LTE RAT switching operation.
Secondly, in the LTE RAT selecting operation or the LTE RAT switching operation described in FIG. 4, the UE may independently perform the fast LTE RAT switching operation or the fast LTE RAT switching operation.
However, the LTE RAT selecting operation or the LTE RAT switching operation described in FIG. 4 has the following problems.
If the UE is located at a region at which an LTE service is impossible at a time at which the UE forcibly transits into an LTE RAT mode, unnecessary LTE RAT mode transition operation and cell search operation are performed since the operation mode of the UE is forcibly transited into the LTE RAT mode even though the LTE service is impossible, so no service interval increases during which the UE does not receive a signal from a Node B, and in a worst case, the UE may not receive a paging message from a network. If the UE is in a weakness-electromagnetic field at a time at which the UE forcibly transits into the LTE RAT mode, the UE fails to register an LTE RAT due to a message transfer failure during a network registration procedure after transiting into the LTE RAT mode since the operation mode of the UE is forcibly transited into the LTE RAT mode even though it is difficult to provide the LTE service, so no service interval increases and the UE may not receive the paging message like a case in which the UE is located at a region at which the LTE service is impossible.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.